The entire disclosure of Japanese Patent Application No. 11-92,715, filed on Mar. 31, 1999, including specification, claims and drawings is incorporated by reference in its entirety.
The present invention relates to an air suspension apparatus so adapted as to improve a riding comfort and stability in operability by appropriately adjusting a damping force of a hydraulic shock absorber in accordance with the running status of the vehicle.
As a suspension apparatus of a vehicle such as an automobile, etc., there is known a so-called semi-active suspension apparatus that is so adapted as to control the posture of the vehicle at a real time with a controller by appropriately adjusting a damping force of a hydraulic shock absorber of a damping force adjusting type in accordance with the status of the vehicle on the basis of information from a vehicle acceleration sensor, a vehicle height sensor and the like. Such a semi-active suspension apparatus can improve a riding comfort and stability in operability as it can alleviate the input due to roughness on a road surface and control a variation in the posture of the vehicle while maintaining the vehicle always at a flat posture.
This conventional semi-active suspension apparatus, however, has the drawbacks that its structure becomes complicated, whereby manufacturing cost for vehicles are increased and the vehicle body becomes heavy because it requires a variety of sensors for use in detecting the status of the vehicle, including an acceleration sensor, a vehicle height sensor, etc., an actuator for shifting a damping force of a hydraulic shock absorber of a damping force adjusting type, and a controller for electronically controlling the operation of the actuator on the basis of information from the variety of the sensors. It further requires wiring for connection of these electronic devices.
The present invention has the object to provide an air suspension apparatus that can readily control the status of a vehicle by appropriately adjusting a damping force of a hydraulic shock absorber in accordance with the status of the vehicle and that has a simplified structure.
One of the features for the air suspension apparatus according to the present invention resides in that it has an air chamber acting as a spring element and a hydraulic shock absorber of a damping force adjusting type capable of adjusting a damping force characteristic by transmitting the pressure of the air chamber and selecting different damping force characteristic on its extending side (i.e. during an extending motion of the hydraulic shock absorber) and on its retracting side (i.e. during a retraction motion of the hydraulic shock absorber), wherein the damping force characteristic of the hydraulic shock absorber presents a hard characteristic on the extending side and a soft characteristic on the retracting side when the pressure in the air chamber is high, while it presents a soft characteristic on the extending side and a hard characteristic on the retracting side when the pressure in the air chamber is low.
With the configuration as described above, the air suspension apparatus according to the present invention can alleviate the input from the axle side (vehicle wheel side) of the air suspension and control a vibration on the vehicle body side of the air suspension by contracting the air chamber acting as a spring element and applying pressure thereto so as to let the damping force characteristic of the hydraulic shock absorber of a damping force adjusting type present a hard characteristic on the extending side and a soft characteristic on the retracting side when the hydraulic shock absorber is retracted from its ordinary status, and by expanding the air chamber and reducing the pressure therein so as to let changing the damping force characteristic thereof present a soft characteristic on the extending side and a hard characteristic on the retracting side when the hydraulic shock absorber is extended from its ordinary status.
Another feature of the air suspension apparatus according to the present invention resides in that, when the pressure in the air chamber for the air suspension apparatus is between the high pressure and the low pressure of the air chamber, the damping force feature of the hydraulic shock absorber of a damping force adjusting type presents a soft characteristic on both of the extending side and the retracting side.
With the configuration as described above, the damping force characteristic for the input of a high-frequency vibration from the axle side of the air suspension presents a soft characteristic both on the extending side and on the retracting side so that the high-frequency vibration from the axle side of the air suspension can be absorbed.
A further feature of the air suspension apparatus according to the present invention resides in that a delay element for delaying the transmission of pressure of the air chamber is mounted in a tubular path transmitting the pressure in the air chamber to the hydraulic shock absorber of a damping force adjusting type.
This configuration of the delay element can provide an appropriate damping force characteristic so that a phase of a variation in pressure to be transmitted from the air chamber to the hydraulic shock absorber can be delayed.
A still further feature of the air suspension apparatus according to the present invention resides in that the delay element is adapted to adjust a phase delay of the variation in pressure to be transmitted via the tubular path in accordance with a frequency of the vibration on the vehicle body side of the air suspension apparatus.
With this configuration as described above, an appropriate damping force characteristic can be achieved by adjusting the phase delay of the variation in pressure to be transmitted via the tubular path in accordance with the frequency of the vibration on the vehicle body side.
A still further feature of the air suspension apparatus according to the present invention resides in that the air suspension apparatus comprises a cylinder with oil liquid (i.e. a hydraulic fluid) filled therein, a piston disposed movably in the cylinder, a piston rod connected to the piston, a passageway through which is allowed to flow the oil liquid by the movement of the piston, a damping force generating mechanism for generating a damping force by controlling the flow of the oil liquid by the association of the movement of the piston, an air chamber so arranged as to vary the inner pressure thereof due to the movement of the piston, and a damping force adjusting mechanism disposed integrally with the damping force generating mechanism and arranged so as to adjust the damping force generated by the damping force generating mechanism upon transmission of the pressure of the air chamber.
This configuration of the air suspension apparatus according to the present invention can provide different damping force characteristics on the extending side and on the retracting side by associated operation of the damping force generating mechanism and the damping force adjusting mechanism. At the same time, it can absorb the high-frequency vibration from the axle side of the air suspension when the pressure in the air chamber is between a higher status and a lower status as the damping force characteristic of the hydraulic shock absorber of a damping force adjusting type presents a soft characteristic both on the extending side and on the retracting side so that the damping force characteristic for the input of the high-frequency vibration from the axle side of the air suspension presents a soft characteristic both on the extending side and on the retracting side.
A further feature of the air suspension apparatus according to the present invention resides in that the air suspension apparatus comprises a cylinder with oil liquid filled therein, a piston disposed movably in the cylinder, a piston rod connected to the piston, a passageway through which is allowed to flow the oil liquid in association with the movement of the piston, a damping force generating mechanism for generating a damping force by controlling the flow of the oil liquid by the associated movement of the piston, an air chamber so arranged as to vary the inner pressure thereof due to the movement of the piston, a damping force adjusting mechanism disposed integrally with the damping force generating mechanism and arranged so as to adjust the damping force generated by the damping force generating mechanism upon transmission of the pressure of the air chamber, and a delay element disposed in the damping force adjusting mechanism so as to delay the transmission of the pressure of the air chamber.
With this configuration, the air suspension apparatus of the present invention can provide different damping force characteristics on the extending side and on the retracting side by the operation of the damping force generating mechanism in associated with the damping force adjusting mechanism, and delay a phase of the variation in the pressure to be transmitted to the hydraulic shock absorber of a damping force adjusting type from the air chamber, so that appropriate damping force features can be realized.
Another feature of the air suspension apparatus according to the present invention resides in that the air suspension apparatus comprises a cylinder with oil liquid filled therein, a piston disposed movably in the cylinder, a piston rod connected to the piston, a passageway through which is allowed to pass the oil liquid by the movement of the piston, a damping force generating mechanism for generating a damping force by controlling the passage of the oil liquid by the movement of the piston, an air chamber so arranged as to vary the inner pressure thereof due to the movement of the piston, a damping force adjusting mechanism disposed integrally with the damping force generating mechanism and arranged so as to adjust the damping force generating mechanism upon transmission of the pressure of the air chamber, and a phase adjusting mechanism for delaying the transmission of the pressure of the chamber, which is disposed in the tubular path for transmitting the pressure of the air chamber into the damping force adjusting mechanism so as to adjust a phase delay of the variation in pressure to be transmitted via the tubular path in accordance with a frequency of the vibrations on the vehicle body side of the air suspension apparatus.
This configuration of the air suspension apparatus according to the present invention can provide different damping force characteristics on the extending side and on the retracting side by the operation of the damping force generating mechanism in association with the damping force adjusting mechanism, and delay a phase of the variation in the damping force characteristics with respect to a variation in pressure of the air chamber when the frequency of the vibration on the vehicle body side of the air suspension apparatus is low, while adjusting the change of the damping force characteristic so as to reach the phase on level with the change of the pressure in the air chamber when the frequency of the vibration on the vehicle body side thereof is high.